Production of dichlorostyrene



Patented Aug. 15,1950 w 2,519,125

omen STATES PATENT some];

I Edwin" R. Erickson, Oak. Park, Ill., assignor to ."Mathieson Chemical Corporation, a corpora",

tionofVirginia 1 No Drawing. Application December 31,1945, Serial'No. 638,579

1 Claim. (01160- 650) 2 This invention relates to a method of treating size of the shot used in air rifles, for example, may halogenated organic compounds containing halobe formed from the paste. If desired, promoters gen on a side-chain attached to an aromatic including alkaline earth metal halides such as nucleus, which mayor may not itself be haloge- ,magnesium chloride, calcium chloride and the nated, whereby all or a' part of the halogen on 5 v like or oxides such as a mixture of zinc, chromium, the side chain is removed'as hydrogen halide. In and cobalt oxides may be .used with the asbestos its most specific aspect, the invention is concerned catalyst.

with the dehydrochlorination of alpha and beta The temperature at which the asbestos catalyst chloroethyl dichlorobenzenes with the producis efiective, other operating factors being astion of dichlorostyrenes. l0 sumed as constant, varies with the material subb A host of materials have been proposed as catjected to the dehydrohalogenation treatment. In alysts'for use in reactions of the above type. Howall cases it is best to efiect the reaction under a ever, manyof these while catalyzing the desired subatmospheric pressure of less than 100 mm. of

. reaction also catalyze ide reactions yielding difmercury absolute. In the dehydrochlorination oi ficultly separable by-products. Others are efchloroethyl dichlorobenzenesto dichlorostyrenes, fective only at temperatures resulting in a major 'I find'it advantageous to operate at temperatures loss of starting material by thermal decomposibetween 300 C. and 400C. and under a subattion or in a major loss of product through polyrnospheric pressure of the order of 10-15 mm. of merization. 'Still others are too costly for use mercury absolute. I f '1 on a commercial scale, either by reason of initial I The asbestos catalyst is easily activated and recost or becausethey are incapable of reactivation activated by burning in a slow stream of air at and re-use: j s I temperatures of from 600 F. to 650 F Itis in- I have now discovered that asbestos is highly active with respect to hydrogen halides and does active as a dehydrohalogenation catalyst where ,not promote the polymerization ofpolymerizable the halogen to be remqvedis attached to a side zacompounds. when employed in the production chain ofan aromatic nucleus. My discovery was of dichlorostyrenes from chloroethyl dichloro made while I was testing the effectiveness of vabenzenes, the proportion of thechloroethyldichlorious dehydrohalogenation, inhibitors in chlor'orobenzenes converted to dichlorostyrenes per pass ethyl dichlorobenzenes at various temperatures over the catalyst is materially; higher than in the and in the presence of'various materials" including -clase of catalysts heretofore employed in the rematerials known to be dehydrohalogenation cataction and since the reaction product contains alysts. Each of the inhibitors effectively arrested only very minor amounts of compounds lower dehydr-ochlorination in the case of these latter boiling than dichlorostyrenesfa Special distillation materials, but when the test was carried out with to remove such compoundsii'either before or folasbestos, the rate of hydrogen chloride evolution lowing separation of the dichlorostyrenes from was substantially the same in the presence or the reaction product is seldom necessary. The absence of any inhibitor. I happened to test asproduct dichlorostyrenes are usually essentially bestos in this connection because of its use in free of objectionable colori'and materials which gaskets, for example, with which chloroethyl diadversely afiect the progress of polymerization chlorobenzes are apt to come into contact during 40 reactions in which dichlorostyrenes are employed their separation from other materials by distillasis-reactants or the'quality of the polymer product. tion. In such a distillation operation, dehydroif The reaction, with the catalyst in the form of chlorination of the chloroethyl dichlorobenzenes shreds or pellets, for example; may be carried with production of dichlorostyrenes is highly unout in any suitable equipment. I generally em desirable because the dichlorostyrenes are prone ploy one or a plurality of appropriately insulated to polymerize to viscouse polymers'capable of u S y p t h y plugging a distillation'column rendering it inopthou th c p u d to be hy o a os a erative. It is thus important that the distillation may initially contact the catalyst as a liquid, I be eiTected in the absence of any material which prefer to completely vaporize the charge matetends toact as a dehydrohalogenation catalyst. rial before bringing it into contact with the cata- In the practice of my invention, commercial lyst. It is ordinarily most convenient to pre-heat asbestos may be shredded and the shreds used the Vapors to a temperature sufiiciently high o as the catalytic material or shredded commercial maintain the catalyst at the desired operating asbestos paper may be reduced to a paste with temperatures. The catalyst-feed ratio may vary water and easily dried pellets having aboutthe within wide limits but usually there is an optirality of tubes, it is unnecessary to. halt the operation for reactivation of the catalyst since one or more of the tubes may be left oil-stream while the catalyst in the remaining'tube or tubes-is subjected to reactivation treatment. Nitrogen, steam or other inert gas may be used to carry the vaporized charge over the catalyst if desired.

My invention is further illustrated by the following examples which are not to be taken as in any way limiting the scope thereof.

Example I Commercial asbestos paper was shredded and made into a moist paste with water. The paste was-pelleted and the-pellets dried over night in an oven; Subsequently the pellets were activated by heating to about 600 C. in a combustion furnace through which a slow stream of air was caused to pass.

Betachloroethyl 2,6-dichlorobenzene was vaporized by heating to a temperature of 450 C. and the vapors passed over the catalyst held at a temperature of 350 C. The rate of liquid feed to the vaporizer was 0.75 ml. per minute. The entire operation was conducted under an absolute pressure of 11mm. of mercury. The product of the dehydrochlorination had a refractive index of 1.5718 at 25 C. as compared with a refractive index of 1.5729 for highly purified 2,6-di'chlorostyrene. This indicates a 90% conversion of the betachloroethy-ld'ichl'orobenzene feed. After the run the catalyst was readily reactivatedby heating in the manner of the initial activation.

Of the twelve isomeric chloroethyldichlorobenzenes. betachloroethyl-2,6 dichlorobenzene is normally the most difficult to' dehydrochlorinat to a dichlorostyrene.

Example. II

Mixed chloroethyl dichlorobenzenes obtained by chlorinating ethyl benzene were vaporized and the. vapors under a pressure of 13 mmof mercury were passed over'the catalyst of Example I maintained at a temperature of 300E320 C. p The product of the dehydrochl'orination showed a side chain chlorine content of 3.33%, and an iodine value of 105.7, indicating a conversion of 72% of the chloroethyl dichlorobenzenes charged.

On fractional distillation of the product material at mm. pressure in the presence of about 0.5% of paranitrosophenol and 1% of alphanitroso betanaphthol to inhibit polymerization of the dichlorostyrenes and d'ehydrochlorfn-ation of unconverted chloroethyl dichlorobenzenes; didichloro'styrenes having refractive indices of from 15780-15518 andboiling points of 70-82 C; were obtained. I EmampZe'II'I In. this instance. the charging rate was twice that of Examples I and 11,. namely. 1.52 mL of liquid per minute and the catalyst temperature varied from313- to 325 C. Samples of the. prodnot taken as the dehydrochlorination progressed showed refractive indices; varying. from 1.5781- 4 1.5768. The product had a side chain chlorine content of 3.5, and an iodine value of 105.4. The percentage conversion of the chloroethyl dichlorobenzenes was again 72%.

On distillation of the crude material in the presence of paranitrosophenol and alphanitroso :betanapthol in the quantities used in the preceding example, dichlorostyrenes having refractive indices between 1.5780 and 1.5800 and boiling points of 76-80 C. at 4.5 mm. were realized.

Example IV The chloroethyl dichlorobenzene mixture constituting the starting material in this run contained about 57.6% of alphachloroethyl dichlorobenzenes and 42.4% betachloroethyl dichlorobenzenes. The catalyst was that used in Examples I, II and III. The liquid chloroethyl dichlorobenzenes were heated to a temperature of 365-370 C. to vaporize them and the catalyst, occupying a space of 113 ml, was thereby held at 315-320 C. The feed rate to the vaporizer was 1. ml. per minute and the operating pressure was 12 mm. of mercury absolute. The product had a refractive index of 1.5769 to 1.5782, an iodine value of 110.3 and a side chain chlorine content of 3.87, representing a dichlorostyrene content of about -77%. On fractionation of av sample of the product at 2-3 mm. pressure in the presence of 0.5% of ditertiary butyl hydroquinone, 1.2% of ditertiary butyl catechol and 0.7% of diamylhydroquinone as inhibitors, only about 1% of material lower boiling than the dichlorostyrenes was found to be present.

Example V Sufficient water was added to a 95:5 mixture of shredded commercial asbestos and magnesium chloridedihydrate to form a paste. The paste was-extruded, cut into pellets. and the pellets fired for two hours at 400 C. Whenmixed chloroethyl dichlorobenzenes were passed over the catalyst thus: prepared, theconditions bein the same as in the preceding example, the conversion to dichlorostyrenes was of the order of 78-81%. The product contained not more than 1.5% of materials lower boiling than dichlorostyrenes.

I Example VI The catalyst. was prepared as in the preceding example except that twice as much magnesium chloride dihydrate was used. The magnesium chloride acts as a promoter. Thedehydrochlorination was carried out. at the same rate and conditions of temperature and pressure as described in Example IV and yielded a product made up of fractions showing refractive indices of from 1.5765 to 1.5800. The product had an iodine value of 114.9 and a side chain chlorine content of 3.04% corresponding to a dichlorostyrene content of from 78.4 to 82%. On analytical distillation the first drop of distillate had a refractive index of 1.5775 and the second drop had a refractive index of 1.5780. This corresponds to less. than 0.25% of objectionable low boiling materials.

Example VII The catalyst in this instance was prepared from a mixture of asbestos, 5% magnesium chloride dihydrate and 5% of anhydrous calcium chloride made to a paste with a minimum of water, extruded and fired as described in Example V. The product from the dehydrochlorination of mixed chloroethyl dichlorobenzenes,

Example VIII The catalyst was prepared from a mixture of 85% of asbestos, of magnesium chloride dihydrate and of anhydrous calcium chloride. The dehydrochlorination was carried out under the conditions of Example IV and gave a product made up of fractions having indices between 1.5768 and 1.5782. The product had an iodine value of 111.2 and a side chain chlorine content" of 3.55 corresponding to about 76-79% of di chlorostyrenes. Low boiling impurities amounted to slightly more than 1%.

Example IX The catalyst was prepared from a mixture of 90% of asbestos, 5% of magnesium chloride dihydrate and 5% of an equimolecular mixture of zinc, chromium and cobalt nitrates converted to oxides on firing for two hours at 400 C. Carrylng out the dehydrochlorination as described in Example IV, samples of the product taken as the reactionprogressed showed refractive indices of 1.5772 to 1.5805. The producct had an iodine value of 117.9,and a side chain chlorine content of 2.93 corresponding to a dichlorostyrene content of 81-83%. pounds were present in the product.

Used in a further run involvin a total charge of 290 ml. of chloroethyl dichlorobenzenes, the catalyst without prior reactivation gave a conversion to dichlorostyrenes of 74-75%.

Eatample X The catalyst of Example IX was used in dehydrochlorinating a mixture of alpha and beta chloroethyl-2, G-dichlorobenzenes, the mixture being essentially free of other isomers. The charge, havinga volume of 45-55 ml., was introduced at a rate of 0.75 ml. of liquid per minute and the pressure was maintained at 10 mm-absolute. During vaporization the charge was preheated to 420-425 C. The catalyst temperature varied between 370-375 C. The index of refraction of the product varied from 1.5685 to 1.5710, corresponding to a dichlorostyrene content of about 60 to 80 per cent.

The catalyst was repeatedly reactivated and reused to dehydrochlorinate additional 45-55 ml. charges of the chloroethyl dichlcrobenzenes until a total of 710 ml. of product was realized from a total charge of 860 ml. On distillation of the crude product under a pressure of 6 mm. in the presence of ditertiary butyl-hydroquinone and ditertiary butylcatechol, pure 2,6-dichlorostyrene having a, refractive index of 1.5729 was obtained.

About 4% of low boiling com- I Example XI The catalyst was unpromoted, being simply shredded commercial asbestos. Using this catalyst under the conditions of the run described in Example IV, the indices of refraction of the fractions making up the product varied from 1.5760 to 1.5770. The product had an iodine value of 98.3 and a side chain chlorine content of 5.18 corresponding to a dichlorostyrene content of 67-70%. About 1% of low boiling compounds were found present on analytical distillation.

As demonstrated by the examples, the catalysts of this invention are remarkably effective in promoting dehydrochlorination of chloroethyl dichlorobenzenes to the desired dichlorostyrenes. Also, as demonstrated, the catalysts are quite long lived, being capable of dehydrochlorinating surprisingly large amounts of charge material without substantial loss of activity from repeated reactivations.

My invention is not limited to the dehydrochlorination of chloroethyl dichlorobenzenes but is generally applicable to dehydrohalogenation reactions where the halogen to be removed is attached to a side chain of an aromatic nucleus. Thus, it may be applied, for example, to the dehydrohalogenation of bromoethyl benzene or other haloalkyl benzenes which are not halo substituted in the nucleus, or it may be applied to the dehydrohalogenation of haloalkyl aromatic compounds, such as, chloroethylor bromoethyl- ,ethylbenzene comprising an alkyl side chain free I of halo substituents.

I claim: In the treatment of a chloroethyl dichlorobenzene to produce the corresponding dichlorostyrene, the method which comprises contacting the chloroethyl dichlorobenzene with a catalytic 1 amount of asbestos under a pressure of the order 01 10-15 mm. of mercury absolute at a temperature between 300-400 C., the asbestos having in admixture therewith minor amounts of an alka- .line earth metal halide and of oxides of zinc,

chromium and cobalt.

EDWIN R. ERICKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,519,125 August 15, 1950 EDWIN R. ERICKSON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 40, for chlorobenzes read chlorobenzenes; line 46, for viscouse read viscous; column 3, line 66, for 1.5518 read 1.5818; column 5, line 30, for producct read product; and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of October, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents. 

